The Catechism lists 11 different subjects under "service." The overall, embracing definition, given by Our Blessed Lord, is given below. The Catechism of the Catholic Church lists, under service: of angels, authority as, civil, deacons as ministers ordained for, family's service as ministry to life, interdependence of creatures and, of lay people in the ecclesial community, liturgy as service of God, of one's country, rendered to civil authorities and to God, as a way to follow Christ. However, the primary definition of service is given by Our Blessed Lord in St. Matthew's Gospel, chapter 22, verses 37, and 39:
Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980
Service: In general, performing one's religious duty as a creature toward God, and fulfilling one's moral responsiblity of meeting the needs of others. To serve God is the primary obligaiton of human beings, personally and socially, to be done in acts of worship and prayer; and in acts of virtue as prescribed by the natural and revealed laws of God. This corresponds to the first three commandments of the Decalogue, and is summarized in the precept to "love the Lord your God with all your heart, with all your soul, and with all your mind" (Matthew 22:37). To serve others is the secondary obligation of a person, deriving from the preceding duty and depending on it. This corresponds to the last seven commandments of god and is synthesized in the precept "You must love your neighbor as yourself" (Matthew 22:39). On these two commandments of serve, Christ says, rest the whole law and the Prophets also.